Chemical changes Flashcards
What pH do acids have?
0-6
Red-yellow
What pH do alkalines have?
8-14
Blue-purple
How can you measure the pH of a solution?
Universal indicator
pH probe attached to pH meter (electronically)
acid + base ->
salt + water
What are titrations used for?
To find out exactly how what volume of acid is needed to neutralise a measured volume of alkali.
What happens when an acid ionises in an aqueous solution?
They produce H+ ions
What are strong acids?
Acids that ionise completely in water, eg. sulfuric, hydrochloric and nitrate acids. All of the acid particles dissociate to release H+ ions.
What are weak acids?
Acids that don’t fully ionise in solution. Only a small proportion of acid particles dissociate to release H+ ions.
What happens for each decrease of 1 on the pH scale?
The concentration of H+ ions increases by a factor of 10.
What is the difference between the strength and concentration of an acid?
acid strength tells you what proportion of the acid molecules ionise in water
acid concentration measures how much acid there is in a certain volume of water
acid + metal oxide ->
salt + water
acid + metal hydroxide ->
salt + water
acid + metal carbonate ->
salt + water + carbon dioxide
acid + metal ->
salt + hydrogen
metal + water ->
metal hydroxide + hydrogen
What is oxidation?
Loss of electrons
What is reduction?
Gain of electrons
What is a redox reaction?
A reaction where reduction and oxidation are happening at the same time
(REDuction and OXidation)
What is an electrolyte?
a molten/dissolved ionic compound which ions pass through in electrolysis
Where will positive ions go in electrolysis?
to the cathode (negative electrode)
Where will negative ions go in electrolysis?
to the anode (positive electrode)
Why can molten and dissolved ionic compounds electrolyse?
they have free ions and can conduct electricity
How can metals be extracted? (two ways)
by being reacted with carbon (if it is less reactive than carbon) through electrolysis (if it is more reactive than carbon)
What are the disadvantages of extracting metals by using electrolysis?
method is very expensive
lots of energy is required (to melt the ore and produce the required current)
If a metal is electrolysed in an aqueous solution, what will be produced at the cathode?
if H+ ions are present and the metal is more reactive than hydrogen, hydrogen gas is produced
if the metal is less reactive than hydrogen, a solid layer of the pure metal will be produced instead (and this will coat the cathode)
If a metal is electrolysed in an aqueous solution, what will be produced at the anode?
if OH- and halide ions are present, molecules of the halide will be formed
if no halide ions are present, the OH- ions (from the water) will be discharged and oxygen gas (and water) will be formed
What do half equations show?
the reaction at one of the electrodes in electrolysis
